The present invention relates to a liquid feed apparatus, in particular to a liquid feed apparatus using a micropump for feeding liquid at a flow rate of several micron litters to several hundred micron litters per second, and also relates to an automatic analyzing apparatus using the liquid feed apparatus.
A micropump has been already known as disclosed in PCT Application WO91/07591. This micropump is composed of three chambers, that is, an inlet valve chamber, and a liquid feed chamber and an outlet valve chamber. Further, the position of an inlet through which fluid flows into the liquid feed chamber is shifted from the center to the peripheral part of the liquid feed chamber so as collect air bubbles on the opposite side where the inlet port is present, within the liquid feed chamber, and an orifice serving as an outlet port is provided in the part in order to remove the air bubbles therethrough. With this arrangement, air bubbles can be efficiently removed from the liquid feed chamber. Further, in order to enhance the shut-off ability of a valve, a thin membrane is formed in a seat part of a diaphragm type valve so as to enhance the close contact between a valve and a valve port.
However, in the structure of the above-mentioned pump, even though air bubbles can be removed from the liquid feed chamber, air bubbles cannot be removed from the outlet valve chamber downstream of the outlet orifice of the liquid feed chamber, that is, it is difficult to completely eliminate affection upon the discharge characteristic of the pump by air bubbles. Further, since the liquid feed apparatus is composed of three chambers, the size in a plan view thereof becomes inevitably large, and accordingly, it is difficult to reduce the cost thereof. The shut-off ability of the valve is enhanced by pressurizing the diaphragm type valve. Accordingly, the operation of the diaphragm type valve at a high frequency is difficult due to a resistance of liquid applied to the diaphragm, and accordingly, the discharge flow rate can hardly be increased up to several hundred micron litters per second.